He was supposed to marry a Spanish woman if I remember correctly which would have made California a Russian colony but took a fall from a horse on the way back home to ask permission to marry and died.

If he hadn't have fallen then America and Russia may have been neighbours on the same continent and may have sorted out their differences way before the Cold War was destined to happen thus negating the need for billions of dollars invested in the nuclear arms race and a stockpile of weapons that ensure the extinction of the human race if every used.

This scenerio comes from Mona Clee's fictional novel "Branch Point" which I don't have with my now and couldn't even find the name of the Russian nobleman myself.

Maybe I can look it up soon but until then I'm off on a trip and probably can't update here for a few weeks so someone take over please.

Wait, wait, wait. You.... don't even know who the guy was at the centre of the implausible Rude-Goldberg-machine-esque alternate reality historical scenario? I foresee a much more challenging and amusing historical quiz game thread opening up.

As a rule, Emperors of Byzantium tended to be blinded after being deposed. While they might have family that would besiege the imperial city on their behalf to restore them, I am unaware of any blind emperor or ex-emperor personally leading the troops forward.

....No. And technically that's not a guess either. I will accept the actual name of the individual, but as it's not common knowledge I'll also take an answer in this format: the __________ of __________. For example: the Count of Flanders, the Earl of Devon, the King of Denmark, the Prince of Muscovy, etc. The event itself was front page news back in the 13th century; I was just never aware of the actual players involved before reading this book.